Electric heaters



Feb. 7, 1961 J. MCORLLY ELECTRIC HEATERS Original Filed July 26,

JNVENTOR. JOSEPH M ORLLY A TTORNE Y ELECTRIC HEATERS Joseph McOrlly, Wilkinsburg, Pa., assignor to Edwin L. Wiegand Company, Pittsburgh, Pa., a corporation of Pennsylvania 17 Claims. (Cl. 53-36) My invention relates to electric heating elements, and

the principal object of my invention is to provide new and improved elements of this character. This application is a continuation of my previously filed applica tion Serial Number. 524,480, filed July 26, 1955, now abandoned. In the manufacture of electric heating elements, a critical operation is the disposition of electrical-insulating heat-conducting material within the metallic sheath of the element to properly space the resistance conductor from the interior wall surface of the sheath.

As the heating element becomes greater in length, the operation becomes more critical. One presently employed method in forming relatively long heating elements is to string the resistance conductor through an insulating tube formed of a multiplicity of spaghettilike tubes of molded or dra'wn refractory material and disposing this assembly within the sheath and thereafter laterally pressing the sheath to compact the refractory material within the sheath.

The described present method has serious limitations in that in very long elements considerable clearance must be provided between the tubular'insulating material and the interior wall of the sheath in order to permit the insulated resistance conductor assembly to be drawn into the sheath without serious obstruction. Also, in machine assembly of the insulated resistance conductor with the sheath, the conductor was largely limited to relatively straight wire form since helical coils would not properly withstand the assembly operations.

Another method presently employed is to gradually fill the sheath with powdered or granular refractory material while holding the resistance conductor centrally of the sheath by mechanical means. This method had limitations insofar as the length of the sheath is concerned.

My invention provides methods and apparatus for producing tubular electrical heating elements in long lengths without the attendant difficulties of the prior art.

In the drawing accompanying this specification and forming a part of this application, there is shown, for purposes of illustration, an'embodiment which my invention may assume, and in this drawing:

Figure 1 is a fragmentary, generally schematic representation of apparatus which may be used in carrying out my invention,

Figures 2 and 3 are enlarged transverse sectional views corresponding respectively to the lines 2-2 and 33 of Figure l,

Figure 4 is an enlarged, fragmentary longitudinal sectional view through the heater sheath, illustrating a theoiy of operation, and

Figure 5 is a transverse sectional view taken throng a completed heater. 7

. Referring to the drawing, the embodiment of the invention herein disclosed is adapted for properly insulating a resistance conductor from .the interior wall of a metallic sheath of long length. The resistance conductor may be in any suitable form, such as a straight wire nited States Patent ice or a helically coiled wire, or a combination, depending upon the power-density requirements of the heater.

As an example, heaters have' been successfully made by use of my invention which have physical specification of a sheath eighty-four inches long, having .165 OD. and .140 ID. The resistance conductor comprised a helical coil of resistance wire, the coil being .060 0.13. It will be understood that the foregoing is merely a specific example and that sheaths longer in length and difierent in diameter have also been successfully filled.

The sheath 10, shown in the drawing, is in the form of a tube of any suitable metal, such as steel, aluminum, copper, or any other metal suitable for sheath purposes in the manufacture of electrical heating elements.

As before mentioned, the resistance conductor 11 may be either in the form of a straight wire or a helical coil and the single dotted line in Figure 1 is intended to represent both.

In preparing the sheath for the filling process, the usual steps of cleaning. and drying the metal tube are preferably carried out, either before or after the resistance conductor is disposed therein.

Preferably, a terminal pin 12 is secured to each end of the resistance conductor in any one of the manners well-known in the art, although it will be appreciated that particularly in the case of a straight wire resistance conductor the opposite ends of the conductor may form the opposite terminals.

The resistance conductor is first assembled with the sheath, prior to filling, and this may be accomplished in any suitable manner. In the manner presently practiced, an apertured plug 14, of a size to closely fit within the opening at what is to be the lower end of the sheath during filling operations, is slipped over a terminal 12, the latter having any suitable abutment to limit insertion of the plug.

The opposite end of the resistance conductor is then inserted into the so-called lower end of the sheath and the resistance conductor is threaded through the sheath in any suitable manner until the opposite end extends outwardly of the upper end of the sheath. At this time the plug 14 will have reached the lower end of the sheath and the plug is tightly inserted into the sheath opening.

The sheath, at its lower end, may be formed with an abutment, such as an inward deformation, to limit the extent of insertion of the plug. Of course, the plug may be formed as a tapered stopper in which event no abutment on the lower end of the sheath is necessary. The plug may be formed of any suitable material, such as compressed refractory, lava, or rubber-like matter, a requirement being that it prevents serious leakage of the insulating material from the lower end of the sheath during the filling operation. As shown in Figure l, with the plug 14in place, the terminal preferably extends outwardly and beyond the plug.

An apertured plug 15 is thereafter slipped over the upper terminal 12 and is inserted within the upper open end of the sheath, the plug 15 being perforated or spiderlike to permit passage of the insulating material therethrough and into the sheath. The plug 15 may be temporary and replaced by a plug similar to the plug 14 after the filing operation. In any event, it is preferable to limit the amount of insertion of the plug 15, and this may be effected by providing an abutment spaced inwardly from the upper end of the sheath. To form such abutment, the sheath may be inwardly deformed to provide an annular rib.

The lengths of the sheath and resistance conductor are related so that the latter is preferably taut when assembled within the sheath as hereinbefore described. In the case of a helical resistor, the length may be such that a little stretching is required during its assembly with the sheath, whereas in the case of a straight wire the length may be determined during assembly.

The sheath, with resistance conductor assembled therewith, is thereafter placed in my improved filling apparatus. The sheath is thereafter filled with a heat-durable, electricinsulating heat-conducting material in a manner and for the purpose of holding the resistance conductor 11 and its terminals properly spaced from engagement with the sheath. Preferably, such material may take the form of a stable refractory material which solidly fills the sheath (except for the resistance conductor) and is compacted during the filling operation and preferably further compacted at a latter stage of manufacture. Magnesium oxide and zircon (crystalline zirconium silicate) have been found suitable for this purpose and may be used in any desired granular or powdered form.

Referring to Figure 1 of the drawing, the lower end of the sheath is held against lateral displacement and for rotation. This may be accomplished by inserting the lower end of the sheath into a conical recess 16 in a stationary block 17 which is suitably mounted on a support (not shown) which may form part of the apparatus.

The sheath is adapted to be revolved about its longitudinal axis and, in the present embodiment, an upper portion of the sheath is inserted between rolls 18 which may be rubber-covered to frictionally engage the sheath and thereby rotate it. Suitable gearing 19 may be employed to rotate the rolls and a motor 20 of any suitable type may have a pulley and belt connection 21 with the gearing.

The upper end of the sheath is aligned with the lower end of a hopper 22 which contains a supply of the refractory material above mentioned. Any suitable valve arrangement may be employed to control flow of refractory material from the hopper.

In accordance with my invention, the sheath and resistance conductor are rotated while a portion or spaced portions of the sheath are displaced laterally from rectilinear alignment.

In the embodiment herein shown, the sheath is bowed by means of a fork member 23 which is either fixedly or adjustably secured to a support (not shown) that may form part of the apparatus. The fork member embraces approximately one-half of the circumference of the sheath and holds the bowed or displaced portion of the sheath against whipping or crank-like motion. Accordingly, it will be appreciated that a portion of the sheath is displaced so that its axis is non-rectilinear and the sheath is rotated about its non-rectilinear axis.

The sheath may be bowed only once, as shown in Figure 1, or it may be bowed in a plurality of spaced portions and the displacements need not be in the same plane. Further, the displacements may be within or without the elastic limit of the sheath, without affecting results in the filling operation although, at the present time, it is believed preferable not to exceed the elastic limit of the sheath during bowing operation. In case the sheath has a plurality of bows, it Will be appreciated that suitable sheath displacement members, such as the forked member 23, may be provided at the desired locations of the bow.

Referring to Figure 1 of the drawing, it will be noted that, although the sheath is bowed so that its longitudinal axis is non-rectilinear, the resistance conductor, because it is somewhat taut, will tend to rectilinear formation. Accordingly, although the opposite ends of the resistance conductor are held generally centrally of the ends of the sheath, an intermediate portion of the resistance conductor is out of central location and may engage a side of the inner wall of the sheath, as shown in Figure 2. Of course, if the sheath is bowed in more than one place, the high point of the displaced portions will be directed toward or against the resistance conductor.

With the sheath in position as shown in Figure l, and bowed laterally in one or more places, the motor 20 is started and granular material from the hopper is directed into the upper end of the sheath. The sheath, as before mentioned, is held to rotation about its non-rectilinear axis, and refractory material entering the sheath gravitates to the lower end thereof, preferably assisting by a vibration of the sheath in any well-known manner.

The sheath fills from the bottom, and vibration tends to compact the refractory material, the latter embedding the resistance conductor and holding it in properly spaced relation from the inner wall of the sheath. After the sheath is filled with refractory material, it is removed from the apparatus. Thereafter, if desired, the plug 15 is replaced by suitable closure means, such as a plug 14, and the heating element thus formed may be subjected to further manufacturing operations in accordance with usual practice.

Referring to Figure 5, it will be seen that the heating element filled in accordance with my invention will have the resistance conductor 11, whether it be coiled or straight wire, embedded in refractory material and held substantially centrally of the sheath 10. Good results have been obtained despite the fact that the sheath was of great length and of very small internal diameter.

Although the theory underlying the successful filling of sheaths of long lengths cannot be described with certainty, Figure 4 of the drawing illustrates What applicant presently believes happens during the filling operation.

Since the bowed sheath is held to rotation about its nonrectilinear axis, the inner wall of the sheath (considering the parts in the plane of the section shown in Figure 2) will move around the off-center resistance conductor. The same effect would result if the resistance conductor shown in Figure 2 would be moved around the inner wall of the sheath 10, for example, in the direction of the arrow so that upon rotation the resistance conductor would be displaced from its full line to its dotted line position.

Now, considering such change of position of the resistance conductor in Figure 4, and keeping in mind that the lower end of the conductor is held centrally located Within the sheath by the plug 14, the relative changing of position of the resistance conductor and sheath wall due to rotation thereof probably takes a conical formation (shown by the curved lines 24 in Figure 4). However, the lower small end of the conical formation is started in central position (by the plug 14) and, therefore, refractory material packs around it. As the refractory material builds up in the sheath, the lower part of the conical formation simultaneously moves upwardly, always being held substantially centrally of the sheath by that part of the resistance conductor which already has been embedded. Whether or not the foregoing theory of operation is correct is immaterial since actual tests have proved the utility of the present invention.

In view of the foregoing, it will be apparent to those skilled in the art that I have accomplished at least the principal object of my invention and it Will also be apparent to those skilled in the art that the embodiment herein described may be variously changed and modified, without departing from the spirit of the invention, and that the invention is capable of uses and has advantages not herein specifically described, hence it will be appreciated that the herein disclosed embodiment is illustrative only, and that my invention is not limited thereto.

I claim:

1. The method of making a tubular electrical heating element, comprising disposing a resistance conductor lengthwise within an elongated tubular sheath in generally taut manner, axially rotating said sheath while a portion thereof is bowed laterally, and filling said sheath with flowable electrical-insulating material during rotation thereof.

2. The method of making a tubular electrical heating element, comprising disposing a resistance conductor lengthwise within an elongated tubular sheath and holding it in generally taut manner, maintaining a portion of said sheath in laterally displaced position so that the axis of said sheath is non-rectilinear, rotating said sheath about its non-rectilinear axis, and filling said sheath with flowable electrical-insulating material during rotation thereof.

3. The method of making a tubular electrical heating element, comprising disposing a resistance conductor lengthwise within an elongated tubular sheath in generally taut manner, maintaining a portion of said sheath in laterally displaced position so that the axis of said sheath is non-rectilinear, rotating said sheath about its non-rectilinear axis, and filling said'sheath with granular refractorymaterial during rotation thereof.

4. The method of making a tubular electrical heating element, comprising disposing a resistance conductor lengthwise within an elongated tubular sheath and connecting its ends to said sheath adjacent to respective open ends of the latter in a manner to hold said resistance conductor generally taut, maintaining a portion of said sheath in laterally displaced position so that the longitudinal axis of said sheath is non-rectilinear and said resistance conductor by reason of its tautness tends to rectilinear formation, and thereafter rotating said sheath about its non-rectilinear axis and filling it from an open end with flowable electrical-insulating material during rotation.

5. Apparatus for filling a tubular sheath which has a resistance conductor extending longitudinallytherein and in generally taut manner and which has a lower end closed, comprising means for maintaining a portion of the sheath displaced laterally so that the sheath axis is non-rectilinear and for holding the sheath for rotation about its non-rectilinear axis, means for rotating the sheath, and means for introducing flowable electric-insulating heat-conducting material into the upper end of the sheath during rotation.

6. Apparatus for filling a tubular sheath which has a resistance conductor extending longitudinally therein and in generally taut manner and which has a lower end closed, comprising a socket for rotatably receiving said lower end and holding the same against lateral displacement, driving rolls for driving engagement with an upper portion of the sheath and for rotating said sheath and for holding such upper portion against lateral displace-, ment, means for laterally displacing an intermediate portion of said sheath so that the axis of the latter is nonrectilinear and for holding said sheath for rotation about its non-rectilinear axis, and hopper means, containing granular refractory material, and having an opening for introducing such granular refractory material into the upper end of said sheath during rotation of the latter.

7. The method of making a tubular electrical heating element, comprising disposing a resistance conductor lengthwise within an elongated tubular sheath, rotating said sheath and said resistance conductor and simultaneously holding end portions thereof against lateral displacement while shifting at least intermediate portions thereof laterally, and filling said sheath with flowable electricinsulating material during rotation thereof.

8. The method of making a tubular electrical heating element, comprising disposing a resistance conductor lengthwise within an elongated tubular sheath, maintaining one end portion of said resistance conductor in spaced relation with the adjacent inner surface of said sheath, rotating said sheath and said resistance conductor and simultaneously holding end portions thereof against lateral displacement while shifting intermediate portions thereof in a lateral direction, and filling said sheath with flowable electric-insulating material from the opposite end during rotation thereof.

9. Apparatus for filling a tubular sheath which has a resistance conductor extending longitudinally therein and in generally taut manner with its opposite ends in spaced relation with respect to the opposite ends of said sheath, comprising means for rotating said sheath and resistance conductor as a unit, means holding end portions of said sheath against lateral displacement, means relativelylaterally shifting intermediate portions of said 1 sheath and said resistance conductor during rotation thereof, and means for introducing flowable electricinsulating material within said sheath during rotation.

10. The, method of making a tubular electrical heating element, comprising disposing a resistance conductor lengthwise within an elongated upright tubular sheath, maintaining the lower end of said resistance conductor in spaced relation with the adjacent inner surface of said sheath, rotating said sheath and resistance conductor while holding end portions thereof against lateral displacement, filling said sheath with flowable electric-insulating material from the upperend during rotation there of, and relatively shifting intermediate portions of said sheath and said resistance conductor in a lateral direction during filling operation. 7

11. The method of making a tubular electrical heating element, comprising disposing a resistance conductor lengthwise within an elongated upright tubular sheath, maintaining the lower end of said resistance conductor in centered relation with the adjacent inner surface of said sheath, rotating said sheath and resistance conductor as a unit while holding end portions thereof against lateral displacement, filling said sheath with flowable electricinsulating material from the upper end during rotation thereof, and relatively shiftingintermediate portions of said sheath and said resistance conductor in an orbital path during filling operations.

12. Apparatus for fill.ng tubular sheath which has a resistance conductor extending longitudinally therein and in generally taut manner, comprising means for rotatably supporting spaced portions of said sheath and for holding such portions against lateral displacement, means for rotating said sheath, means for maintaining at least a portion of said sheath intermediate said spaced portions in laterally displaced relation, and means for introducing flowable electric-insulating material Within said sheath during rotation of the latter.

13. Apparatus for filling tubular sheath which has a resistance conductor extending longitudinally therein and in generally taut manner with its opposite ends in centered relation with respect to the opposite ends of said sheath, comprising means for rotatably supporting said opposite sheath ends and for holding such ends against lateral displacement, means for rotating said sheath, means for maintaining at least one intermediate portion of said sheath in laterally displaced position sutficient to cause engagement of said resistance conductor with an interior surface of .said sheath, and means for introducing flowable electric-insulating material within said sheath during rotation of the latter.

14. Apparatus for filling electric heating elements of the type having a resistance wire embedded in powder insulating material within a substantially rectilinear tubular sheath, comprising a frame structure for supporting said sheath in an upright position including means for holding opposite ends of said sheath against substantial movement transverse to the longitudinal axis of said sheath, a filler member adapted to hold said powdered insulating material and communicating with the upper end of said sheath to supply said material therein, and means for displacing an intermediate portion of said sheath from said longitudinal axis and for maintaining it displaced from said axis during the filling of said sheath with said powdered insulating material.

15. The method of making a tubular electrical heatingelement, comprising disposing a resistance conductor lengthwise Within a substantially rectilinear elongated tubular sheath, holding end portions of said sheath against substantial movement transversely of the longitudinal axis of said sheath and displacing an intermediate portion of said sheath in a direction transverse to and removed from the previous substantially rectilinear axis of said sheath, and maintaining said intermediate sheath portion displaced position from said axis to thereby de- 7 form said longitudinal axis from its substantially rectilinear form during filling of the sheath from an end with fiowable insulating material.

16. The method of making a tubular electrical heating element of the type having a resistance wire embedded in powdered insulating material Within a tubular sheath, which comprises disposing the resistance wire longitudinally within an upright an unfilled sheath and supporting said wire in centered relation at opposite ends of said sheath and in generally taut lengthwise condition, and causing a relative transverse shifting between said resistance wire and the interior surface of said sheath in a direction peripherally of said interior surface during filling of said sheath With said insulating material from an upper end thereof.

17. The method of making a tubular electrical heating element of the type having a resistance wire embedded in powdered insulating material and disposed Within a tubular sheath, which comprises disposing the resistance wire longitudinally within an upright and um filled sheath and supporting said Wire in centered relation at opposite ends of said sheath and in generally taut lengthwise condition, and causing a relative circular shifting between said resistance wire and the interior surface of an intermediate portion of said sheath during filling of said sheath with said insulating material from an upper end thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,754,003 Johnson-Vea et al. Apr. 8, 1930 2,032,957 Simmons Mar. 3, 1936 2,316,683 Finlayson et a1. Apr. 13, 1943 2,319,573 Abbott May 18, 1943 

